Effect of graphene oxide and friction stir processing on microstructure and mechanical properties of Al5083 matrix composite

In this study, the surface nanocomposite containing graphene oxide was produced on the Al5083 alloy surface, using Friction Stir Processing (FSP) in liquid cooled condition, in order to improve the microstructure and mechanical properties. For this purpose, FSP was carried out up to 3 passes on a base alloy with and without reinforcing particles. Microstructural features and mechanical properties of the obtained surface nanocomposite, FSPed Al 5083 and base alloy were investigated. In order to study the microstructure, Electron Back Scatter Diffraction (EBSD) was used. It was revealed that the grain size nanocomposite was about 1 μm after the process. This was while the grain size of the specimen with no reinforcement, after the process was 6 ± 1.1 μm and the size of the base alloy was 23 ± 2.3 μm. The substantial effect of the reinforcing particles in preventing the grains growth in the nanocomposite specimen was the main reason for this difference. Study of mechanical properties of base alloy, FSPed specimen, and the nanocomposite revealed that the simultaneous use of cooling environment and performing the process, increased the hardness of stir zone compared to the base alloy. This increase was raised in the presence of graphene oxide particles and reached to 123 ± 1.7 HV. It was also observed that the nanocomposite had a better tensile behavior than the base alloy and the FSPed specimen. SEM images of the fracture surfaces indicated the existence of dimples and voids at the surface of the base alloy specimens and the FSPed specimen which showed their ductile fracture, but at the nanocomposite surface, in addition to the ductile fracture, a brittle fracture was occurred

Hot rolling of MWCNTs reinforced Al matrix composites produced via spark plasma sintering

Aluminum/CNT nanocomposite sheets, with appropriate dispersion and interfacial bonding, were fabricated by a combination of powder metallurgy, spark plasma sintering (SPS), and hot rolling. The effects of CNT content as well as plastic deformation, on the microstructure and mechanical properties of the obtained nanocomposite, were investigated. The composite reinforced by 0.5 wt.% CNTs showed an optimal dispersion of CNTs into the aluminum matrix after both SPS and hot rolling. Minimum CNT damage and minimum carbide formation were observed after hot rolling. The best comprehensive mechanical properties corresponded to the sheet of Al-0.5 wt.% CNT nanocomposite thanks to the strong interfacial bonding between Al and CNTs, full densification of the nanocomposites as well as the uniform dispersion of the CNTs into the aluminum matrix. Hardness measurements showed that the maximum hardness was obtained for sheets containing 1.5 wt.% CNTs in both the as-SPS and the as-hot rolled conditions. Load transfer, Orowan, and grain size strengthening mechanisms could affect the increase of strength as well as the combination of strength and ductility of the sheets of Al-CNT nanocomposites. Aluminum/CNT nanocomposites were hot rolled without reinforcing damage. The optimal dispersion of 1.5% CNTs led to increased mechanical properties